while I'm not sure what's causing your problem, I'd speculate that this is Entourage's way to accepting "push notifications". That popup is coming up because it's trying to create a listener. If you don't need push notifications, you can probably disable them to silence the popup. If your mail is set to check every 10 minutes, and someone sends you an email, your entourage won't see it until the next time it checks its mail if push notifications are disabled. (up to a 10 minute delay, for most people, not a big deal)
